Simulated drought regimes reveal community resilience and hydrological thresholds for altered decomposition
Future climate scenarios forecast a 10–50% decline in rainfall in Eastern Amazonia. Altered precipitation patterns may change important ecosystem functions like decomposition through either changes in physical and chemical processes or shifts in the activity and/or composition of species. We experimentally manipulated hydroperiods (length of wet:dry cycles) in a tank bromeliad ecosystem to examine impacts on leaf litter decomposition. Gross loss of litter mass over 112 days was greatest in continuously submersed litter, lowest in continuously dry litter, and intermediate over a range of hydroperiods ranging from eight cycles of 7 wet:7 dry days to one cycle of 56 wet:56 dry days. The resilience of litter mass loss to hydroperiod length is due to a shift from biologically assisted decomposition (mostly microbial) at short wet:dry hydroperiods to physicochemical release of dissolved organic matter at longer wet:dry hydroperiods. Biologically assisted decomposition was maximized at wet:dry hydroperiods falling within the range of ambient conditions (12–22 consecutive dry days) but then declined under prolonged wet:dry hydroperiods (28 and 56 dry days. Fungal:bacterial ratios showed a similar pattern as biologically assisted decomposition to hydroperiod length. Our results suggest that microbial communities confer functional resilience to altered hydroperiod in tank bromeliad ecosystems. We predict a substantial decrease in biological activity relevant to decomposition under climate scenarios that increase consecutive dry days by 1.6- to 3.2-fold in our study area, whereas decreased frequency of dry periods will tend to increase the physicochemical component of decomposition.
KeywordsClimate change Leaf litter decomposition Resilience Dry:wet cycles Tank-bromeliad ecosystem
We thank the members of the Laboratoire Environnement de Petit Saut (HYDRECO) for technical support and the use of their facilities, and A. Compin (CNRS, UMR ECOLAB, Toulouse), M. Fichaux and F. Petitclerc (CNRS, UMR ECOFOG, Kourou) for field assistance. Financial support was provided by the Agence Nationale de la Recherche throughout the Rainwebs project (Grant ANR-12-BSV7-0022-01), an “Investissement d’Avenir” Grant (Labex CEBA, ref. ANR-10-LABX-25-01), and a CNRS Grant to the Groupement De Recherche International “Environmental Forcing on Freshwater biodiversity and ecosystem functioning” (GDRI EFF). We thank Dr. Kneitel and two anonymous reviewers for constructive criticism on an earlier version of this paper.
Author contribution statement
HRP, CL, J-FC, BC, DSS, RC conceived and designed the experiment, HRP, GB, CL, J-FC, BC, RC performed the experiment. HRP, GB, DSS analyzed the data, HRP, DSS, RC wrote the manuscript, and all authors contributed critically to the drafts and gave final approval for publication.
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